I recently installed an Icom 2100h with an NMO hole in roof mount on the Focus. The radio is powered through direct leads to the battery and is mounted to plastic.

On receive, if I'm in the 2300-3500 RPM range, I will get a little whine through the radio. The whine increases when the RPM's increase. When I'm in gears 4 and 5, I either don't hear the noise or it isn't there. The noise is most prevalent in gears 1-3. I have not checked to see if I transmit the whine yet.

It really does make listening difficult so I would like to combat this noise. Will a filter fix my problems? What kind of filter should I use? Where should it be connected?

The chances are good that it is a ground loop. Make double sure you have a good connection at the NMO. In a lot of cases, the insulation under the roof, and the paint layer cause a condition where the coax shield at the mount doesn't make a good connection.

Sometimes, not often, grounding the chassis of the radio will cause a ground loop as well. That's an easy test, obviously.

Probably not. Alternator whine can indeed be caused by a bad diode in the alternator, but if there is one, you'd already know it.

The next thing to do is put it into a dummy load. If you still have the whine, make sure the chassis isn't grounded to a seat rail or whatever, via its mounting hardware. After that, if you still have it, look at the output of the alternator, and see if it looks even and sinusoidal without any gaps. Just for the record, very few alternators go bad these days. Occasionally, you get a leaky diode, but even that won't cause audible whine in a 12 diode, dual wound, alternator.

If you connect it to a dummy load, and the noise goes away, then look for a bad coax connection somewhere along the way.

Before I go rooting around above the headliner again let's make sure we have done as much diagnosis as we can.

The power comes off the battery, through the firewall, and into a distribution block where it feeds a power amplifier and some various toys. The amp is not an amp for the ham radio. So, everything that pulls power, comes off of this block. The Icom has it's own dedicated ground back to the battery while the other gear is just grounded to the chassis.

Could this be the source of my problem?

The radio sits in a very snug hole in the dash so it's not mounted to anything really. Plastic surrounds it, and yes I do check the temps in there.

What is a good way to check the connection between the roof and the antenna? I'll try a continuity tester as a first guess.

Alan, thanks for all your info, here and on your site. I tried to base my install around good practices but apparently I missed one or two.

A ground loop is any condition, where in there is a differential voltage between two, otherwise common connections. It may be a positive or negative connection. Here's an example.

Let's say we have a RigRunner powering everything except the radio which runs directly to the battery. And let's also say, the RigRunner IS NOT grounded the same place as the radio (battery), but instead is grounded to a hard place on the chassis (seat rail maybe). The ground for the RigRunner will have a different potential than the ground for the radio. If any device, amplifier, monitor, whatever, is plugged into the RigRunner, and the radio, then they too will have a potential between their respective connections.

Vehicle manufacturers prevent ground loops by using common power and ground connections for the various devices. For example, both headlights are grounded to the same point, not different points on the chassis. All of the connections for the ABS, all run back to a common point. the same things happens on all in-vehicle connections. this is especially important on vehicle which incorporate data busses (almost all new ones do).

I know this sounds a bit wordy, but it points out a very important item with respect to amateur radio installations (or any electronics really); they must have common connection points! This includes power and ground! When they don't...

I had the same problem with that radio several yrs ago. I returned it to HRO, and that in itself is another story and got another, it did the same thing, I had it in a fairly new S-10 blazer 1 yr old maby, I could take the yaesu ft-2200 out of my wifes car and hook it up same power leads, ant, ect no noise but with the Icom still had the whine. After trying everything in the book I sold it at a hamfest and went on. btw shortly after that Icom came out with the IC-2200. Every now and then you can hear someone on 2 meters talking with the same whine, and I would bet there on a IC-2100. 73 Patrick

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